I'd look at this Dayton: Dayton Audio RSS315HF-4 12" Reference HF Subwoofer 4 Ohm High Fidelity Reference Series 295-464
And if you had a bit more power, I'd consider a pair of these TC Sounds Epics: TC Sounds Epic 12" DVC Subwoofer 293-650
Not that they wouldn't do well on the lower power, I just think they'd do phenomenal off 1200w or so.
Also, maybe even these T3, not sure about the build quality on them, I'd ask around though. They're a good deal: http://www.parts-express.com/pe/show...number=269-088